Age hardening austenitic steel



United States O 2,799,577 AGE HARDENING AUSTENITIC STEEL Reinhold Schempp, Clay, Peter Payson, New York, and

Joe Gin-Young Chow, Long Island City, N. Y., assignors to Crucible Steel Company of America, New York, N. Y., a corporation of New Jersey N Drawing. ApplicationiFebruary' 18,1953,

Serial No. 337,688

2 Claims. (Cl. 75"128) This invention pertains to improvements in austenitic steels, and provides a relatively high carbon, high phosphorus, steel of this type which is age hardenable to a minimum of C 32 and up to about C 50 Rockwell depending upon the analysis, and which is further characterized by high strength and corrosion resistance at both room and elevated temperatures.-

application is a continuation-in-part of our copending' application Serial No. 294,260, filed June 18, 1952, now Patent No. 2,686,116, issued August 10, 1954.

Objects of this invention are: to provide austenitic age hardenable steels which are useful for applications where high strength at room temperature combined with low magnetic permeability are required, as for studs, gears, crankshafts, and so on, in non-magnetic power plants of submarines: for retainer rings on rotors of electric generators; and so forth; also where hardness and resistance to softening at elevated temperatures upward of 1300 F. combined with good resistance to oxidation and'corrosion at such temperatures are required, particularly in combustiori products of leaded gasoline, as for automotive eX-- haust valves, valve seats, and similar parts; and finally, where high strength at temperatures upward of 1100" F. is required together with resistance to oxidation at these temperatures, as for steam power plant and gas turbine parts.

Another object of this invention is to provide an aus- "ice nickel, manganese and chromium in order to assure that the steel will have the requisite minimum age hardenability of the C 32 Rockwell.

That the minimum carbon and phosphorus contents are particularly critical in this respect is shown by the data contained in the following Tables I to IV, inc.

Table I LOW CARBON AUSTENITIC STEELs WITH PHOS- PHO RUS [Sol'rifion treated at 2150 F. and 2300 F and water uenched; aged at 1200; 1300"; 1400 F. for 16 hours?] Bar o Mn P Si Ni V or N' as;

3915 05 1. 5 .10 .40 11.1 18.0 .26 Fe 3918 .05 1.4 .27 .37 11.3 18.8 .21 Fe O Rockwell Hardness Bar 3915 Bar 3918 2,150 2,300 2,150 2,300 F. F. F. F.

As solution Treated 8 7 6 Aged 1,200 F.16 h0ur 8 7 8 8 Aged 1,300 F.16 hours. 8 7 20 21 Aged 1,400 F.16 hours 9 8 19 19 Evidently although some hardening is attainable in the above low carbon steel containing about 0.27% P, the

tenitic steel which is hardenable to a minimum of C- 32 Rockwell, or 300 Brinell.

Another object of this invention is to provide an austenitic a'ge hardenable steel which can be hardened to a minimum of C 32 Rockwell by use of a solution temperature no higher than 2200 F.

disclosed austenitic steels containing: 0.4 to 1.5% carbon; 12 to 30% chromium; 0 to 25% nickel 0.1 to 25% manganese; the combined nickel and manganese content comprising 8 to 28%; 0 to 5% silicon; balance substantially iron, which are age hardenable to at least C 32 Rock- Well by 2 heat treatment consisting 6f 5011111011 treating at about 2300 F. and quenching, and thereupon aging at about 1300 F. An apprecibale deterrent to the use of such hardened steel is the very high s'olutiontemperature required. Even with modern furnace equipment-and design it is not easy to heat treat large quantities of parts at such high temperatures, particularly if the parts are siz'eable'. Furthermore, the s'olidus temperature of such steel is not much above 2350 F. Thus the'solution temperature is dangerously close'to the temperature at which the steel begins to melt, and there is considerable hazard therefore in the handling of such steel at the tem-' perature-require'd for proper solution treatment for the desired hardening.

Now we have discovered that by introducing about 0.15 to 0.45% phosphorus into steel of approximately the composition given above, the necessary solution temperature I Table II EFFECT or 0 ()NY ATTAINABLE HARDNESS IN AUSTEN- ITIC O-Mir-Ni-Cr STEE'LS CONTAINING PHOSPHORUS [Specimens s'olution'treated at 2150 F., water quenched, and aged at 1250 for 16 hours] Analysis Percent-Balance Fe "0 Rockwell Hardness Bar 0 M11 P' Si I Ni Cr N As After Quonch'ed Aging 9.1 .21 1.3a 2.2 20.3 e 29 9,8 .21 .83 4. 0 22. 0 44 9.0 .21 .90 3.7 20. (i 45 f 5.1 .34 549: g 3.8 21.6 31 4,9 ,33 .40 3.8 21.5 :4 7 5.1 .36 .58 3. 8 21. 6 49 1,4 .23 .44 ,13;.3 13.0 33 3, 2 18 .39 9. 1 18.3 34 3.2 .23 .40- 9'.-2 18.6 35 1.2 .38 13.1 17.5 36 3.4 .22 .38 9.1 18.3 37 3.5 .32 .40 9.2 18.6 41 1.3 ,9 4 .40 13,1; 18,3 40 1.4 V .34 .35 13.0 18.1 42

The effect of phosphorus'on' the attainable hardness of the s'teelafter a solution treatment at 21503-13. and aging at 1250 F. is shown in Table III and Table IV, 5

3 Table III EFFECT OF PHOSPHORUS ON ATTAINABLE HARDNESS OF MEDIUM CARBON AUSTENITIO Mn-Ni-Cr STEELS [Specimens solution treated at 2150 F., water quenched, and aged at I 1300" F. for 16 hours.) l.

EFFECT OF PHOSPHORUS ON ATTAINABLE HARDNESS OF HIGH CARBON AUSTENITIC O-Mn-Ni-Or STEELS {Specimens solution treated at 2150 F., water quenched, and aged at 1250 F. for 16 hours] Rockwell B Analysis Percent-Balance Fe Hardness 0 Mn P Si Ni Cr N As After Quenched Aging From the data of Tables IIIV, inc., it will be seen plus manganese content may be lowered to about 9%,

as evidenced by bar 3902.

The upper limit for carbon is established by forgeability, and for forgeable steels of the invention, is set at about 0.8%. For castings the carbon may range as high as about 1.5%. Thus, the broad range for carbon is about 0.2 to 1.5%, or about 0.2 to 0.8% for the forgeable analyses. The preferred range for the forgeable alloys is about 0.3 to 0.8%.

With increasing phosphorus, the forgeability of the steel likewise decreases, and therefore the upper limit is set at about 0.45% P for the wrought material. However, for cast material we may employ as high as 1% P. The lower limit is set at about 0.15% P to assure adequate age hardening.

Manganese may be present over the range of 0.5 to 15%, and nickel over the range of about 3 to the sum of these two being present within a broad range of 9 to and within a narrow range of about 12 to 30%. As above noted, the broad range is applicable to analyses containing upwards of 0.3 carbon and the narrow range 'to analyses containing lower carbon contents down to about 0.2%

Table V EFFECT OF PHOSPHORUS ON THE SOLUTION TEMPERATURE NECESSARY FOR DEVELOPING ADEQUATE HARDNESS IN C-lldn-Ni-Cr AUSTENITIO STEEL [Specimens quenched from indicated solution temperature and aged at 1250 F. for 16 hours.)

O Rockwell Hardness Analysis Percent-Balance Fe Bar 1,900 F. 2,000 F. 2,150 F.

0 Mn P Si Ni 0: Mo N As Aged As Aged As Aged Quenched Quenched Quenched that all analyses containing at least 0.3% carbon together with at least 0.15 phosphorus, age harden adequately, i. e.,- to a minimum of C 32 Rockwell. On the other hand, analyses containing carbon below 0.3% and down to about 0.2% necessitate a carfeul balancing of the minimum carbon plus phosphorus and nickel plus manganese contents to assure this minimum age hardenability. Thus, it will be seen from the data for bars 4488'4495, at the bottom of Table 11, that if the carbon plus phosphorus totals at least 0.45 together with a nickel'plus manganese total of at least 12%, the steel will age harden to upwards of C 32 Rockwell. On the other hand, if these requirements are not met for the analyses containing less than 0.3% carbon, the steel will not harden to the required minimum of C 32 Rockwell, as evidenced by reference to the results for bars 3900 and 3965 of Table II. With carbon upwards of 0.3%, the minimum nickel Furthermore, whereas with the low phosphorus steels of the copending application it is necessary to cool rapidly as in a water quench from the solution temperature in order that the desired hardness may be attained in the steel after it is aged, we have found that when phosphorus over about 0.15% is present in the steel, the desired hardness over C 32 Rockwell maybe attained in the steel after aging even though the cooling rate from the solution temperature is somewhat retarded as in an oil quench, or even an air cool of sections under about 1 inch thick. This obviously is of considerable advantage in the heat treatmentof large sections which would suffer much less distortionwhen quenched in oil than when quenched in Water.

The efiect on'age hardenability of varying chromium contents of the-steel of the invention is shown by the following Table VI:

Table VI "EFFECT OF CHROMIUM ON AT'IAINABLE HARDNESS or gggn rgrrro G-Mn-Ni-Cr STEELS CONTAINING rnos- [All specimens solution treated at 2150 F., water quenehed,.and aged at 1300" F. for 16 hours] Analysis Percent-Balance Fe Rockwell C Hardness Bar As Aged at C Mn P Si N1 Cr Quenehed 1,300 F.,

16 Hrs.

1\I magnetic; all others non-magnetic.

As shown by the above data, the chromium content must be at least about 10% in order to impart the minimum 5 a stable austenitic structure substantially free of ferrite.

When the steel is to be used under high stress at elevated temperature we generally include up to about 3% of either one or both of the carbine forming elements molybdenum and tungsten.

Nitrogen is generally over .03-% in the steel of the .invention and maybe present up to about 0.40%.

Since the steel may be machined in the hardened condition after final heat treatment, we may include sulfur in the steel composition up to about 0.30% to improve machinability.

We may use diiierentproportions of the elements carbon, manganese, phosphorus, silicon, nickel, chromium, molybdenum (or tungsten), and nitrogen in the steel depending on the application. For an application requiring a non-magnetic material with high room temperature strength and good ductility, we generally balance the composition so that the carbon is on the low side of the range and nickel is present in larger amounts than manganese. Data on some compositions suitable for such an application are given in Table VII.

Table VII MECHANICAL AND BERMEABILITY PROPERTIES OF STEELS FOR NON-MAGNETIC HIGH STRENGTH APPLICATION Analysis Percent-Balance Fe Bar 0 M11 P Si N1 Cr N [Pieces in sq. section solution treated as indicated; aged at 1300 F. for 16 hours; and machined to tensile, im-

pact, and permeability test pieces] O 0.2% Tensile Elong. Red. V-Notch Permea- Bar Solution Treat- Rock. Yield, Strength, in 1.4 Area, Izod, bility, 'ment Hard. p. s. i. p. s. 1. ln., Percent FtJ-Lbs. H=500 Iercent 3941 2,050 F. Water- 34 88,000 146, 000 27. 9 2,150 F. water 38 116, 000 167, 000 17. 6 1, 950 F. watch-.- 36 106,000 155, 000 22. 2 1,950 F. air 35 100, 000 152, 000 24. 4 2,050 F. water.... 41 132, 000 175, 000 15.0 2,050 F. watch-.. 33 88, 000 149, 000 24. 7 2,150 F. water- 42 126, 000 177, 000 18. 4 1 950 F. Water 121, 000 7, 0 18. 1 1,950 F. 39 109, 000 160, 000 20. 7 2,150 F. 35 105, 000 155, 000 23.0 150 F. 35 107, 000 153,000 17. 2 200 F. 39 128, 000 171, 000 11. 5 950 F. 33 100, 000 145, 000 22. 9 050 F. 39 124, 000 166, 000 21. 5 150 F. 36 103, 000 155, 000 19. 4 150 F. 36 105, 000 155, 000 21.0 950 F. water 34 104, 000 149,000 18.6 950 F. air 33 92,000 143, 000 22.7 050 F. water- 40 125, 000 166, 000 17.1

required age hardenability of C 32 Rockwell. The

preferred lower limit for the chromium content is about 12%, as the steels of the invention containing upwards of 12% chromium are found to be less brittle in the age hardened condition than those containing lesser chromium contents. An upper limit of 30% is set for the chromium (35 The low permeability steels of the foregoing type having good forging and age hardening characteristics together with high strength, have the following preferred range of analysis: carbon about 0.2 to 0.5%; phosphorus about 0.2 to 0.4%, the sum of carbon and phosphorus being at least 0.45%; manganese about 1 to 5%, nickel about 8 to 15%, the sum of nickel and manganese being at least about 12%; chromium about 17 to 25%; silicon up to about 1%; nitrogen up to about 0.3%; sulfur up to about 0.3%; balance substantially all iron.

For steel to be used for automotive exhaust valves and similar parts, we generally balance the composition with carbon in'the middle of the range and manganese in larger amount than nickel, although we may also use a high percentage of nickel as shown in the analysis of bar 4123 sum of manganese and nickel so that the steel will have in the table below.

Table VIII PROPERTIES OF STEELS SUITABLE FOR EXHAUST VALVE SERVICE Analysis Percent-Bel. Fe Rock. Weight Loss Sol. Treated: in Ber 2,150 F., Lead Oxide Aged; at 1,675 F., 0 Mn P S1 Ni Or N 1,300 F., hrs. gmsJsqJin.

Steels of the foregoing type which are age hardenable to Table IX-Continued a minimum of C 38 Rockwell on solution treating at a STRESS RUPTUR PROP IE 0 temperature no higher than 2200 F., and subsequent D ERT S AT L200 aging at about 1300 F., have the following preferred range of analysis: Carbon about 0.4 to 0.7% phosphorus Bar ,gggg stress &2? gg? :233: about 0.15 to 0.45%; manganese about 1 to 12%; nickel ment p. s. 1' Hours Perceiit tion about 3 to the sum of manganese and nickel being Area from about 9 to chromium from about 20 to 30%; silicon up to about 3%; nitrogen up to about 0.4%; sul- 888 33 fur up to about 0.3%; metal of the group molybdenum BO 561000 203 5. 7 "15:0 and tungsten up to about 3%; balance substantially iron. g5 gg ggg 3g ff 32 For applications where strength at high temperatures BO 56, 000 184 16.3 20.0 for long time service is required, we generally include 2% 1883 g; s molybdenum (or tungsten) in the composition as stated B0 0 6 20.7 27.5 BO 62,000 204 above. Some data on steels sultable for high temper- BO 56,000 527 as 5 ature applications such as steam power plant and gas turbine parts are given in Table IX.

Table 1X PROPERTIES OF STEEL SUITABLE FOR SERVICE AT 1200 F. UNDERSTRESS 2 N ore-Test piece with 60 degree V-notch, diameter base of notch Heat treatments: BB2150 F., water quench; aged 1500 F.-16 hours. BO2150 F., water quench; aged 1300 F.16 hours; plus 1700 F.-2 hours;

.252 in. with gage section .357 in. diameter; .005 in. radius base of notch.

Anl B 1 F Bar 8 ms Percent a mm 9 A preferred range of analysls for steels of this type is: 6 Mn s Ni or carbon about 0.45 to 0.7%; phosphorus about 0.2 to 0.45%; manganese aboutS to 12%; mckel about 4 to 18%; 5 ,23 4 22 2 g chromium about 20 to 30% silicon up to about 3 metal F g g gg-g i-g of the group molybdenum and tungsten, about 1 to 3%; 715 .43 .38 7.5 21.2 1 nitrogen up to about 0.4%; sulfur up to about 0.3%; balance substantially iron. ROOM TEMPERATURE PROPERTIES It is of interest that the steels of this invention are quite resistant to 'overaging. Although the optimum Heat r'gfi Tensile 3 3? fig i k aging temperature 'for maximum hardness is about Bar ge st Strength, i g '1250/1300 F. good hardness 1s developed with aging ment 5.55 can 51M temperatures as high as 1500 F. Furthermore, steel I which has been aged at 1300 F. can be reheated for 3933--.. BB 35 98,000 156,000 18.6 25.0 7 a short time at temperatures as high as 1700" F. without 2555:: 2% 5f? fijggg 22% 23:5 suffering much losls of hljiirdness. Some data on It; B0 33 000 1401000 6 5 v sistance of the stee s of t s lnvention to so emng a g temperatures are shown in Table X.

Table X EFFECT OF HIGH TEMPERATURE ON HARDNESS OF CMnPNl-Cr [Specimens solution treated at 2150 F., water quenched, and aged as indicated] Analysis Percent-Balance Fe O Rockwell Hardness v Aged, are are S Ni Cr Mo 3 1, s.; 0 Mn P 1 Q 16 hours 16 hours 16 hours Reheated,

1,700 F 2 hours What we claim is:

1. Age hardenable austenitic steel characterized in being hardenable to a minimum of about C 32 Rockwell after solution treatment at a temperature no higher than 2200" F. and subsequent aging at about 1300" F. for about 15 hours, said steel consisting essentially of about: 0.2 to less than 0.3% carbon and 0.15 to 1% phosphorus, the sum of carbon and phosphorus being at least 0.45%; 0.5 to 15% manganese; 3 to 25% nickeL the sum of nickel and manganese being about 12 to 30%; 10 to 30% chromium; up to about 3% silicon; up to about 3% of metal selected from the group consisting of molybdenum and tungsten; up to about 0.4% nitrogen; up to about 0.3% sulfur; and the balance iron.

2. A precipitation hardened, austenitic alloy steel, hav- 10 ing a hardness of at least C 32 Rockwell, said steel consisting essentially of about: 0.2 to less than 0.3% carbon and 0.15 to 1% phosphorus, the sum of carbon and phosphorus being at least 0.45%; 0.5 to 15% manganese; 3 to 25% nickel, the sum of nickel and manganese being about 12 to 30%; 10 to 30% chromium; up to about 3% silicon; up to about 3% of metal selected from the group consisting of molybdenum and tungsten; up to about 0.4%

nitrogen; up to about 0.3% sulfur; and the balance iron.

References Cited in the file of this patent UNITED STATES PATENTS 2,523,917 Payson Sept. 26, 1950 2,528,637 Clarke Nov. 7, 1950 2,686,116 Schempp et a1 Aug. 10, 1954 

1. AGE HARDENABLE AUSTENTIC STEEL CHARACTERIZED IN BEING HARDENABLE TO A MINIMUM OF ABOUT "C" 32 ROCKWELL AFTER SOLUTION TREATMENT AT A TEMPERATURE NO HIGHER THAN 2200* F. AND SUBSEQUENT AGING AT ABOUT 1300* F. FOR ABOUT 15 HOURS, SAID STEEL CONSISTING ESSENTIALLY OF ABOUT: 0.2 TO LESS THAN 0.3% CARBON AND 0.15 TO 1% PHOSPHORUS, THE SUM OF CARBON AND PHOSPHORUS BEING AT LEAST 0.45%; 0.5 TO 15% MANGANESE; 3 TO 25% NICKEL, THE SUM OF NICKEL AND MANGANESE BEING ABOT 12 TO 30%; 10 TO 30% CHROMIUM; UP TO ABOUT 3% SILICON; UP TO ABOUT 3% OF METAL SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM AND TUNGSTEN; UP TO ABOUT 0.4% NITROGEN; UP TO ABOUT 0.3% SULFUR; AND THE BALANCE IRON . 